The present invention generally relates to equipment for cooling a liquid and, more particularly, is concerned with a vertical multi-tube falling film type heat exchanger having an arrangement for providing improved liquid distribution at an inlet head of the heat exchanger.
Various types of heat exchangers have been used for cooling liquids. One type called a vertical falling film heat exchanger has an outer shell in which are disposed a plurality of vertical tubes in a side-by-side spaced array extending between and connected at their opposite ends to tube sheets attached across top and bottom ends of the shell.
Also, the heat exchanger has upper and lower hemispherical shaped heads attached to the upper and lower tube sheets to define flow manifolds which communicate with opposite open ends of the tubes respectively above and below the tube sheets at the top and bottom ends of the outer shell. An inlet is attached to the upper head and an outlet is attached to the lower head. The liquid to be chilled or cooled flows from the inlet, through the upper head, to and through the interiors of the vertical tubes, from the tubes into the lower head, and out the outlet.
Further, the outer shell of the heat exchanger has a lower inlet and an upper outlet for circulation of a refrigerant, such as ammonia, through the outer shell upwardly along the exteriors of the vertical tubes. To cool the liquid, heat must transfer from the liquid flowing downward within the tubes, through the walls of the tubes, to the refrigerant flowing upward along the exteriors of the tube walls. In order to provide for rapid chilling of the liquid, it is necessary that the liquid flow in a thin film on the inner surface of the tubes. As can be appreciated, this will cause the liquid to quickly give off its heat to the refrigerant in the outer shell and achieve the desired temperature with a single pass through the heat exchanger.
In one application of the heat exchanger in the beverage industry, the requirement is to cool or chill a liquid, such as water, from approximately 70.degree. F. to 80.degree. F. at the heat exchanger inlet down to about 34.degree. F. at its outlet. However, difficulties have been encountered in lowering the temperature of the water below around 40.degree. F.
One cause of the difficulties is inadequate distribution of the liquid, such as water, to all of the tubes. If the liquid is not distributed evenly, then some tubes will be flooded with liquid, others partially flooded with liquid, and still others starved of liquid, resulting in suboptimal heat transfer. Another cause is inadequate control of liquid flow into and down the tubes. Some of the liquid falls through the tubes without contacting the tube walls and so does not flow as a thin film down the interior of the tube walls which would optimize the transfer of heat from the liquid to the refrigerant.
Another type of known heat exchanger is the plate-type heat exchanger which comprises a large number of corrugated sheets or plates that are gasketed together.